There are several known systems for communication between the topside of an oil and/or gas well and tools located further down in the oil and/or gas well. Moreover, it is known to supply such tools with electric energy from the topside.
US 2004094303 describes an inductively coupled method and apparatus for communication with wellbore equipment. Here it is shown a well pipe comprising inductive elements near or in the inner surface. The inductive elements of the well pipe are connected by means of a wire etc to the topside of the well.
A well tool comprising inductive elements in its outer surface may be lowered into the well pipe and positioned so that there is an inductive connection between the inductive elements of the tool and the inductive elements of the well pipe. Hence, signals can be transferred between the tool and the well pipe. However, both the inductive element of the well pipe and the inductive element of the well tool comprise a radial electrical winding. Consequently, the magnetic flux that is generated by a current flowing in the electrical windings of the inductive elements has a direction circumferentially around the well pipe.
The disadvantage of this technology is that since the inductive elements are provided in or near the inner surface of the well pipe, they are exposed to wear and damages due to friction and impacts from equipment lowered into and elevated out from the well. Moreover, the inductive coupling between the induction elements of the well pipe and the tool is rather poor, resulting in a low bandwidth.
NO 324328 describes another system for transferring power and signals between a well pipe and a tool lowered into the well. Here, the signal is induced into the well pipe by means of inductive elements provided radially around the well pipe.
US 2002057210 describes a method and system for subsurface logging utilizing a modified metallic tubular having an elongated body with tubular walls and a central bore adapted to receive a support member. The tubular including slotted stations to provide through-tubular signal transmission and/or reception. Pressure barrier means provide hydraulic isolation at the slotted stations. The support member is equipped with various sources and sensors, including an antenna adapted to generate a magnetic dipole moment with a transverse or controllable orientation, and adapted for engagement within the tubular.
US 20040056663 describes a method and apparatus for a downhole antenna comprising a housing having an outer surface and a longitudinally bored inner cavity, the outer surface having a first slot and a corresponding second slot extending from the outer surface to the longitudinally bored inner cavity; a first removable downhole antenna segment disposed in the first slot in a first transverse cross section of the housing, the first removable downhole antenna segment comprising at least one coil to inductively couple a signal from the longitudinally bored inner cavity to the earth formation.
The object of the present invention is to provide a well tool and a well pipe where the inductive elements are less vulnerable for wear and damages. Moreover, it is an object of the invention to provide a well tool and a well pipe where the electromagnetic communication between the inductive elements of the well tool and the well pipe is improved.